1. Field of the Invention
This invention relates generally to gravity flow dryers for particulate material and, more particularly, to a multi-stage gravity flow dryer for particulate material.
2. Summary of the Prior Art
It is often necessary or desirable to dry freshly harvested grain before it is processed or stored. Storage of grain with excess moisture may cause quality deterioration and spoilage during subsequent storage.
The need to dry grain prior to storage has long been recognized in the art and many grain drying systems have been developed to accomplish this purpose. In many such prior systems, the grain is heated by air at a predetermined temperature during a first drying process and then the grain is quickly cooled to a desired storage temperature by exposing the grain to a flow of ambient air. One such system is the cross-flow column type grain dryer in which grain flows downwardly by gravity through a column having perforate walls and heated air is forced transversely through the perforate walls of the column to contact the grain to dry the grain or remove moisture. Typical of such cross-flow grain dryers are the grain dryers shown and described in U.S. Pat. No. 2,732,630 to Markowich and U.S. Pat. No. 3,238,640 to Fry.
While the prior art cross-flow type grain dryers are generally effective in drying grain, the entire quantity of grain is not uniformly dried. A further drawback associated with this type of prior art drying quantity of grain is not uniformly dried. A further drawback associated with this type of prior art drying system has been that the rapid temperature change occurring as a result of exposing the wet grain to a flow of high temperature air has tended to result in stress cracking of the grain. Although several different attempts have been made to improve the cross-flow grain dryers to alleviate stress cracking, as well as to improve the quality of the grain, such attempts have had mixed success and have resulted in greater complexity in the grain drying structure. The present invention provides a multi-stage cross-flow type grain dryer which provides a greater uniformity of drying of the grain, while minimizing the problems associated with stress cracking of the grain.